Missing 3d text on animation render
I found the answer by myself. The issue was caused by linked data on copy-pasted text. I didn't know that copying an object linked the original and it's copy propierties. When I animated the copies that I then modified as new text, I was animating the originals too. By deleting copies keyframes, I was deleting the ones which animated the originals. And by changing copies colour, I was changing original's colour.

I also learnt that duplicating (shif+d or alt+d) is better than copy-pasting